The invention relates to measuring and testing equipment, and more particularly to a precision instrument which utilizes variations in a signal from a strain gauge or other form of transducer to indicate a dimension or position.
Dial indicators, precision gauges and other measuring instruments in many forms are well known. For example, a standard for a long time has been a mechanical indicator sold under the trademark "Last Word" by the L. S. Starrett Company of Athol, Mass. An indicator of this type is placed in a drill chuck, for example, and the chuck is rotated slowly by hand while a finger of the indicator is engaged against a pin or bore, for locating the pin or bore on the center of rotation of the drill. Variations in the needle position of the mecanical indicator were noted as the chuck was rotated. The indicator was fairly accurate, but since it was used with the drill chuck hand rotated, it could not be completely accurate. When a machine spindle is not powered and rotating in the way it will be when performing a desired operation, there are slack effects and oil film effects in the spingle bearings which can give different readings from what occurs in the dynamic mode of operation.
Other dial indicators for generally the same purposes have been quite expensive, particularly those that have been the most sensitive. For example, a dial indicator sold under the name BesTest was graduated to 0.0001 inch. The operation of this dial indicator was mechanical, somewhat similar to the Last Word indicator.
Electronic indicators have also been in general use but have been far more expensive as compared to mechanical indicators. A number of such indicators are manufactured by Mitutoyo Mfg. Co. Ltd. of Japan, distributed in the United States by MTI Corporation of Paramus, N.J. For example, one Mitutoyo indicator adapted for some of the purposes of the present invention is the Digi-Matic indicator Model No. 543-162, shown on pages 13A-13B of the Mitutoyo Measuring Instruments Catalog No. 6000.
Such modern electronic indicators are very expensive principally because they use position-sensing transducers which are in themselves very costly components.
There has been a need for a relatively simple and inexpensive precision electromechanical measuring device for performing center finding functions and other position locating and dimension checking functions with a high degree of precision, and this is a principal object of the present invention described below.